It is known to protect a vehicle occupant with an inflatable protection device, such as an air bag, that is inflated in the event of sudden vehicle deceleration such as occurs in a vehicle collision. The air bag helps to protect the vehicle occupant by restraining the movement of the occupant during the collision. The air bag is inflated by inflation fluid provided by an air bag inflator. The inflation fluid may include gas stored under pressure inside a closed container in the inflator. Typically, an electrically actuatable, pyrotechnic initiator is triggered by a collision sensor in the vehicle to cause the container to open and release the stored gas to inflate the air bag.
If the pressure of the stored gas in the container in the inflator drops below a predetermined pressure level, the air bag may not inflate properly. For this reason, it has been proposed to monitor the pressure level of stored gas in an air bag inflator using some type of pressure sensor.